The Long Term Evolution (LTE) network consists of the Evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (E-UTRAN) Evolved Node B (eNB) and the Evolved Packet Core (EPC). The network is flattened. The EUTRAN includes a collection of eNBs which are connected with the EPC via the S1 interface. The eNBs can be connected with each other via the X2 interface. The S1 and X2 interfaces are logical interfaces. One EPC can manage one or multiple eNBs. One eNB also can be controlled by multiple EPCs, and one eNB can manage one or multiple cells. The EPC consists of the Mobility Management Entity (MME), the Serving Gateway (SGW) and the Packet Data Network Gateway (PGW).
In the LTE, due to the factors such as the wireless environment, or the movement of a User Equipment (UE) in the network coverage areas etc., exceptions may occur to the connection of UE. For example, it may cause RLF to the UE, thus affecting the normal service of the UE. The RLF reason needs to be detected as soon as possible in order to avoid such situation. For example, whether any coverage holes exist in the coverage area needs to be detected. However, the improper switching parameters in the LTE network also may cause the UE to have an RLF. For example, a serving cell may switch the UE to a neighbor cell which has weak signal, so that RLF occurs to the UE in the neighbor cell. In order to optimize such situation, the Mobility Robustness Optimization (MRO) is proposed in the Self-Organizing Network (SON) function of the LTE. The MRO can find the problems of the current mobility parameters according to the behavior that RLF occurs to the UE. For example, as shown in FIG. 1, RLF occurs to the UE which locates in cell 1 (eNB1). And finally, the UE selects a cell 2 (eNB2) to initiate reestablishment. Cell 2 (eNB2) can immediately send an RLF Indication (RLF INDICATION) to cell 1 (eNB1) according to a reestablishment message of the UE. If the reestablishment of the UE fails in cell 2, and the UE returns to an IDLE state, the UE can select a new cell 3 to implement a Radio Resource Connection (RRC) establishment via cell selection. However, while the UE is in the IDLE state, the UE may pass through multiple cells. From the time when RLF occurs to the UE to the process that the RRC is established, the information collected by the UE is very important for the network side to detect whether it is the problem of coverage or the problem of mobility parameters.
However, as mentioned above, as the coverage hole may cause the UE to have the RLF, it may cause that the network side cannot accurately judge the RLF reason. For example, the time from the time point that the UE returns to the IDLE state due to unsuccessful RRC establishment to the time point that the UE selects a proper cell to implement successful RRC establishment via the cell selection can be very long or very short. And, this is relative to the movement track of the UE and the size of the coverage holes. However, the current information reported by the UE only include the measurement result at the time when RLF occurs to the UE, which can only be used to judge whether the RLF is caused by the coverage. Thereby, the RLF reason cannot be accurately judged.